The present invention relates to a method of forming a monomolecular film on a liquid surface and an apparatus for overlaying the same as a single-layered or multilayered film on a solid state substrate.
Presently a solid state electronic device, whether active or passive, mainly comprises a thin-film electronic material. In the manufacture thereof, the thin-film technology is being targeted for further refinement. That is, there is an expectation of developing new applications of thin-film technology because thin-film technology is actually becoming the key to success in much of the electronics industry. Under these circumstances, the role played by organic thin-film materials is now only becoming more important, wherein rapid progress is being made in the development of functional thin-film materials aimed at achieving a higher added value exceeding the limit of inorganic materials. Particular attention is being given to the technique for the preparation of a monomolecular single-layered or multilayered film (L-B film) as an organic thin-film.
An apparatus for preparing an L-B film as shown in FIG. 4, for example, has been employed. However, such a conventional apparatus and the method of using such an apparatus each have a serious defect. For example, the preparation of a single-layered film or a multilayered film (L-B film) requires the formation of a stable solid-state film on a liquid surface from a monomolecular film substance, and maintaining fluidity on an appropriate level, not only in the well-known horizontal deposition method of forming an L-B film, but also in the vertical dipping method. When using a long-chain fatty acid as a component of an L-B film, overlaying can be easily accomplished if the metal ions of the metal salt of that long-chain fatty acid are binary metal ions, whereas, if they are triad metal ions, a hard film without fluidity is formed, thus making it extremely difficult to overlay the film on a substrate.
This finding is supported by "I. Languir, et al., J. Am. Chem. Soc., vol. 59 (1936)" and "M. Sugi, Solid-State Physics, vol. 17, No. 12 (1982)."
The development and application of L-B films, when using long-chain fatty acids, is therefore limited to those having binary ions, and this constitutes a hindrance to achieving technical progress in the development of L-B films. In fact, the actual situation is that almost no progress has been made in research on the development of L-B films using a long-chain fatty acid containing triad metal ions.
In the conventional L-B film forming apparatus, as shown in FIG. 4, because of the very small width of the solid-state substrate (B), to be vertically immersed, relative to the inner width of the trough (A), a disturbance is caused in the monomolecular film on the liquid surface, and this makes it extremely difficult to form a film in a normal state. Monomolecular film material flows around the substrate (B), thus producing a non-uniform film on the liquid surface. As a result, a hard film cannot form from this flow.
Because of this flow, even when a film has been formed on the substrate, the thus obtained film does not maintain the molecular configuration that it had on the liquid surface. Even by keeping a prescribed surface pressure on the liquid surface by means of a barrier, factors such as the coupling force between the trough inner walls and the monomolecular film material prevents the surface pressure from remaining uniform, and as shown in FIGS. 6(a) and 7(a), the monomolecular film material flows in a disturbed state.
For these reasons, a film formed on the substrate, if any, is defective.
These defects have been reported in "B. R. Malcon, Thin Solid Films, 134 (1985) 201-208," and the present inventor confirmed the fact both in theory and in experiments.